Alexander of Aphrodisias, the most famous commentator on Aristotle, wrote 500 years after Aristotle's death, at a time when Aristotle and Plato were rather forgotten minor philosophers in the age of Stoics, Epicureans, and Skeptics. He defended a view of moral responsibility we would call libertarianism today.

Greek philosophy had no precise term for "free will" as did Latin (liberum arbitrium or libera voluntas). The discussion was in terms of responsibility, what "depends on us" (in Greek ἐφ ἡμῖν). Alexander believed that Aristotle was not a strict determinist like the Stoics, and Alexander himself argued that some events do not have predetermined causes.

In particular, he held that man is responsible for self-caused decisions, and can choose to do or not to do something. This appears to be not very different from the Stoic Chrysippus' idea that one can assent or dissent to an action. Chrysippus said actions are pre-determined (fated) but not necessitated.

Alexander denied three things - necessity (ἀνάγκη), the foreknowledge of fated events that was part of the Stoic identification of God and Nature, and determinism in the sense of a sequence of causes that was laid down beforehand (προκαταβεβλημένος) or predetermined by antecedents (προηγουμένος).

Alexander on Chance

Most of the ancient thinkers recognized the obvious difficulty with chance (or an uncaused cause) as the source of human freedom. Both Aristotle and Alexander describe chance (ἡ τύχη) as a "cause obscure to human reason"

Alexander makes it clear that the role of chance is to break the causal chain of determinism. If this means that some things happen at random and "for no reason" (μάτην) then so be it. And the randomness is ontological, not merely the result of human ignorance.

Alexander is not being original here. He is reading Aristotle as denying the Leucippean necessity. Epicurus denies necessity even more clearly with his "swerve."

Leucippus said,

Nothing occurs at random, but everything for a reason and by necessity.

οὐδὲν χρῆμα μάτην γίνεται, ἀλλὰ πάντα ἐκ λόγου τε καὶ ὑπ’ ἀνάγκης

Aristotle clearly accepts that things happen at random. In his Metaphysics he makes the case for chance as an uncaused cause (causa sui).

Nor is there any definite cause for an accident (συμβεβηκός), but only chance (τυχόν), namely an indefinite (ἀόριστον) cause.

Without such indefinite (uncaused) causes, everything would happen by necessity.

It is obvious that there are principles and causes which are generable and destructible apart from the actual processes of generation and destruction; for if this is not true, everything will be of necessity: that is, if there must necessarily be some cause, other than accidental, of that which is generated and destroyed. Will this be, or not? Yes, if this happens; otherwise not.
(Metaphysics, Book VI, 1027a29)

For Alexander, as for Aristotle, a random event "for no reason" provides a fresh start or new beginning (ἀρχή) of a causal chain (ἄλυσις) that can not be traced back indefinitely. This effectively puts an end to the Stoic ideas of foreknowledge and pre-determination.

These new beginnings are associated with chance (τύχη) and happen by themselves (αῦτόματος)

If Stoic pre-determinism is true and there was but a single choice, men would deliberate "for no reason" (μάτην). (De Fato, XI-XII)

Chrysippus calls assent a choice (προαίρεσισ). Perhaps inconsistently with his Stoic doctrine of fate, Chrysippus thinks alternatives are possible in some sense.

Alexander says that what gives man the power of a rational assent is the existence of new beginnings. He goes to the extreme of making this the essence of humanity (sounding very Hegelian),

To be rational (λογικῷ) is nothing other than to be the origin (ἀρχή) of one's actions.
(De Fato, XIV, 184.15)

For man is the origin (ἀρχή) and cause (αίτια) of actions that happen through him (δι’ αὐτοῦ)
(De Fato, XV, 185.11)

Alexander says that these origins allow agents to do otherwise in the same circumstances (τῶν αὐτῶν περιεστώτων) at another time (ἄλλοτε). (De Fato, XV, 185.8)

Doing otherwise requires the existence of real alternative possibilities. Unfortunately, Alexander does not see that the role of chance is merely to generate these possibilities, creating new causal chains which can be evaluated for the best choice of action.

Alexander on the Causal Chain of the Stoics

(R. W. Sharples translation)

[The Stoics] say that this universe, which is one and contains in itself all that exists, and is organised by a Nature which is alive, rational and intelligent, possesses the organisation of the things that are, which is eternal and progresses according to a certain sequence and order; the things which come to be first are causes for those after them, and in this way all things are bound together with one another. Nothing comes to be in the universe in such a way that there is not something else which follows it with no alternative and is attached to it as to a cause; nor, on the other hand, can any of the things which come to be subsequently be disconnected from the things which have come to be previously, so as not to follow some one of them as if bound to it. But everything which has come to be is followed by something else which of necessity depends on it as a cause, and everything which comes to be has something preceding it to which it is connected as a cause. For nothing either is or comes to be in the universe without a cause, because there is nothing of the things in it that is separated and disconnected from all the things that have preceded.

a single uncaused event would make the universe collapse

For the universe would be torn apart and divided and not remain single for ever, organised according to a single order and organisation, if any causeless motion were introduced; and it would be introduced, if all the things that are and come to be did not have causes which have come to be beforehand [and] which they follow of necessity. And they say that for something to come to be without a cause is similar to, and as impossible as, the coming to be of something from what is not. The organisation of the whole, which is like this, goes on from infinity to infinity evidently and unceasingly.
(De Fato, XXII, 191.32-192.18)

the famous "causal chain"

...all the things that are become causes of some of the things after them, and that in this way things are connected to one another by the later being attached to the earlier in the manner of a chain (ἄλυσις), this being what they propose as the essence as if it were of fate.
(De Fato, XXII, 193.5-193.8)

Alexander on Logical Determinism

The present truth value of statements about the future was an important argument that occupied Aristotle (the "sea-battle" of de Int. IX), Epicurus, and the Stoics. It was thought by many to demonstrate the necessity of fate. But it is dismissed as mere words by some commentators, Carneades, for example. Alexander says those who make this argument are childish or joking, and do not know what they are talking about.

[The Stoics make] the argument that the proposition 'there will be a sea-battle tomorrow' can be true but not also necessary; for what is necessary is what is always true, but this [proposition] no longer remains true when the sea-battle comes to be; but if this is not necessary, neither is what is signified by it of necessity, [namely] that there will be a sea-battle. But if there will be a sea-battle, but not of necessity (since it is true that there will be a sea-battle, but not [true that there will be a sea-battle] of necessity), clearly [there will be a sea-battle] contingently; and if contingently, the coming-to-be of some things contingently is not done away with by the coming-to-be of all things in accordance with fate.

But this [is an argument] of those who both jest and do not know what they are talking about. For neither is everything that comes to be of necessity necessary, if what is necessary is the eternal, but what comes to be of necessity has been prevented from being like this by its very coming-to-be; nor is the proposition that asserts this [sc. what comes to be of necessity] necessary, if what is signified by it is not of this sort [sc. necessary]. (For we do not describe every proposition, in which what is necessary is contained, as ipso facto] necessary; for it is not in this way that it is judged that a proposition is necessary, but by its not being able to change from being true to being false.)

If then [the proposition that asserts what comes to be of necessity] is not necessary, it has not at all been prevented from being true, just as 'there will be a sea-battle tomorrow'. For, [even] if [when] stated as [something] necessary it is not true because of the addition of the necessary, if it does not become necessary by the addition of 'of necessity' it will still be true in the same way as [the proposition] uttered without this addition. But if this is true, when the next day arrives the proposition that 'a sea-battle came to be of necessity' will be true; and if of necessity, not contingently.

And indeed, if 'there will be a sea-battle tomorrow' is true, it will always be the case that a sea-battle came to be in accordance with fate, if indeed all the things that come to be are in accordance with fate. But if in accordance with fate, unalterably, and if unalterably, it cannot not come to be, and it is impossible for that not to come to be which cannot come to be; and how can we say that that for which it is impossible not to come to be can also not come to be, since it is necessary for that to come to be for which it is impossible not to come to be? So all the things that come to be in accordance with fate will be of necessity, according to them, and not also contingently, as they say in jest.
(De Fato, X, 177.7-178.8)

XXII-XXV. Causation and the unity of the universe. (R. W. Sharples translation)

XXII. Now that we have first considered these points, it would not be a bad idea to set alongside them those which they actually make concerning fate, and to see whether there is any such force in the latter as to make it reasonable, on account of their closeness to the truth, to disregard in this way even the clear facts of the matter. But our discussion of these points will only be to the extent to which it is useful for the purpose before us.

Well then, they say that this universe, which is one and contains in itself all that exists, and is organised by a Nature which is alive, rational and intelligent, possesses the organisation of the things that are, which is eternal and progresses according to a certain sequence and order; the things which come to be first are causes for those after them, and in this way all things are bound together with one another. Nothing comes to be in the universe in such a way that there is not something else which follows it with no alternative and is attached to it as to a cause; nor, on the other hand, can any of the things which come to be subsequently be disconnected from the things which have come to be previously, so as not to follow some one of them as if bound to it. But everything which has come to be is followed by something else which of necessity depends on it as a cause, and everything which comes to be has something preceding it to which it is connected as a cause. For nothing either is or comes to be in the universe without a cause, because there is nothing of the things in it that is separated and disconnected from all the things that have preceded. For the universe would be torn apart and divided and not remain single for ever, organised according to a single order and organisation, if any causeless motion were introduced; and it would be introduced, if all the things that are and come to be did not have causes* which have come to be beforehand [and] which they follow of necessity. And they say that for something to come to be without a cause is similar to, and as impossible as, the coming to be of something from what is not. The organisation of the whole, which is like this, goes on from infinity to infinity evidently and unceasingly.

There is a certain difference among the causes, in expounding which they speak of a swarm of causes, some initiating, some contributory, some sustaining, some constitutive, and so on (for [our] need is not at all to prolong the argument by bringing in everything they say, but to show the point of their opinion concerning fate). — There are, then, several sorts of cause, and they say that it is equally true of all of them that it is impossible that, when all the circumstances surrounding both the cause and that for which it is a cause are the same, the matter should sometimes not turn out in a particular way and sometimes should. For if this happens there will be some motion without a cause.

Fate itself, Nature, and the reason according to which the whole is organised, they assert to be God; it is present in all that is and comes to be, and in this way employs the individual nature of every thing for the organisation of the whole. And such, to put it briefly, is the opinion they lay down concerning fate.

XXIII. The falsity of what they say needs no arguments or refutations from elsewhere, but is evident from the statements themselves. For what clearer refutation of a statement could there be than that it does not fit the things about which it is made? The first statement, at any rate, that all the things that are become causes of some of the things after them, and that in this way things are connected to one another by the later being attached to the earlier in the manner of a chain, this being what they propose as the essence as if it were of fate — how is this not clearly in conflict with the facts? For if fathers are causes of their children, and enquiry after causes should be governed by considerations of affinity, so that the cause of a man is a man, and of a horse a horse, of which of those after them are those who never even married in the first place the causes? Of whom are those children that die before maturity the causes? For many of the things that come to be, because of their falling short in size, either are not roused or perish too early, and so do not succeed in becoming the causes of anything in accordance with the potential that they possess. What will they say is caused by the superfluities that grow on certain parts of the body? What by monstrosities and things which come to be in a way contrary to nature, which cannot even survive in the first place? But if the outer husk in plants is for the sake of the inner husk and the inner husk for the sake of the fruit, and if they are watered so that they may be nourished and nourished so that they may bear fruit — even so, one can find many things in them which do not come to be in this way. For of what subsequent things would one say that those fruits which have rotted or dried up are the causes? Of what the fact that certain leaves are double? From these points it is obvious to those who want to see the truth and are able [to do so] that, just as not all that has potential exercises it, so not everything that might become a cause either is already a cause or has become one or will become one; indeed, it is not the case that everything that has come to be is at once, in virtue of its being, already the cause of something that will be in the future.

To say on the one hand, in engaging with their opponents, that these things too are causes, but retreat to the claim that it is not clear of what they are the causes (as, indeed, they are often compelled to do in connection with the Providence of which they speak, too) is the tactic of those who are trying to find an easy way out of their difficulties. For by using this argument it will be possible to say of all the most absurd things that they both exist and have causes which are in accordance with reason, though still obscure to us.

XXIV. Is it then the case that, if this is how these things are, something will come to be without a cause, and does our argument give support to this? Or is it possible to preserve [the thesis] that nothing comes to be without a cause, even though matters are as we state? For if we abandon the chain of causes and cease saying that, when certain things have first come to be, it follows of necessity that they must by nature become causes, as if [being] causes were included in their essence, and [if instead we] assign causes starting from the things that are coming to be and are subsequent, and, further, look for the causes in the proper sense of the things that are
coming to be, we will find both that nothing that comes to be comes to be without a cause, and that it is not, on account of this, the case that everything that comes to be will be of necessity, in accordance with the sort of fate described.

For it does not follow of necessity that, just because Sophroniscus exists, he must therefore be a father and the cause of some one of those after him. If however Socrates is to exist, of necessity Sophroniscus is the cause of his coming-to-be. If a foundation exists, it is not necessary for a house to come to be, but if a house exists the foundation must necessarily have been laid first; and it is in this way that one must understand that the causes are of necessity in the things that come to be by nature too, not that it follows of necessity that the things that are first should be causes of something, but that those that come to be subsequently must of necessity have one of the things preceding them as a cause.

And there are some things among those that come to be that are of such a sort as to have a cause, indeed, not however one that is proper to them and primary*, but [rather], as we are accustomed to say, [one that is] accidental. The finding of treasure by someone who was digging in order to plant has the digging as a cause, indeed, but it is not [a cause] proper to it and did not come to be on account of it. For causes in the strict sense are followed by what is caused either of necessity, as our opponents think, or for the most part; but causes that are accidental in this way rarely become causes of such things.

So if one argues in this way it follows that one both says that nothing comes to be without a cause and preserves the coming-to-be of some things as a result of luck and fortuitously, and the existence of what depends on us and the contingent, in the realm of facts and not just as expressions.

XXV. For how is it not clearly false to say that everything that follows something derives the cause of its being from it, and that everything that precedes something is its cause? For we see that not all the things which succeed one another in time come to be because of those which have come to be earlier and before them. Walking is not caused by standing up, nor night by day, nor the Isthmian /games by the Olympian, nor yet summer by winter. And for this reason one might wonder at their making the assignment of causes in such a way that they always regard what has come to be first as the cause of what follows it and construct a successive connection and continuity of the causes, and [at their] giving this as the explanation for nothing's coming to be without a cause.

For we see that in many cases the same thing is the cause both for the things that come to be first and for those that come to be later. At any rate, the cause of standing up and of walking about is the same; for standing up is not the cause of walking about, but the cause of both is the [man] who stands up and walks about and his choice.

And we see that night and day, too, which have a certain order in relation to each other, have one and the same cause, as does similarly the changing of the seasons. Winter is not the cause of summer, but both the former things [night and day] and the latter things [winter and summer] are caused by the motion and rotation of the divine body* and the inclination along the ecliptic; the sun, moving along this, is the cause of all alike of the things mentioned above.

Nor indeed does it follow that, because night is not the cause of day nor winter of summer, and these things are not intertwined with one another in the manner of a chain, they therefore come to be without a cause, or that if they did not come to be in this way [sc. in the manner of a chain] the unity of the universe and of the things that are and come to be in it will be torn apart. For the heavenly bodies and their rotation are sufficient to preserve the continuity of the things that come to be in the universe. Nor indeed is walking without a cause, [just] because it does not derive its cause from standing up.

So the sequence of causes of which they speak would not be a reasonable explanation to give of nothing's coming to be without a cause. For as motions and times have some cause indeed, though the cause of a motion is not the previous motion nor of a time the previous time, so it is with the things that come to be in them and through them. For the continuity of the things that come to be has a cause, and it is on account of this that the universe is one and eternal, always organised in one and the same way; and one should look for this and not leave the cause aside. But one should not suppose that it is of such a sort as this, [namely] that what is younger comes to be from what is older, as we see is the case with the coming-to-be of living creatures.
It is reasonable, too, to say that there is some first beginning among the causes, which has no other beginning or cause before it.

For it is not the case that, if all things that come to be have causes, therefore all things must necessarily have causes. For not everything that is comes to be. How is it not absurd to say that the causes and the sequence and successive connection of them extend to infinity, so that there is nothing that is first or last? For to say that there is no first cause is to do away with cause; for if the first beginning is done away with it is necessary that what follows it be done away with. And knowledge too would be done away with by this argument, if knowledge in the proper sense is acquaintance with the first causes, but according to them there is no first cause among causes.
Nor does every transgression of an established order do away with the things in which it occurs: for it is not impossible that some things should come to pass in a way that conflicts with the monarch's order, but not therefore be altogether destructive of his monarchy. Nor, if something of the sort happens in the universe, does it at once follow that it altogether destroys the happy state of the universe, just as that of the house and its master is not [altogether destroyed] by some negligence or other on the part of the servants.